Versioned rule table
Approved rules used by the calculator. Exactly £100,000 is at threshold, not over.
| Rule | 2025/26 | 2026/27 |
|---|---|---|
| Tax year | 6 April 2025–5 April 2026 | 6 April 2026–5 April 2027 |
| Standard Personal Allowance | £12,570.00 | £12,570.00 |
| Personal Allowance taper begins | ANI over £100,000 | ANI over £100,000 |
| Personal Allowance reaches zero | £125,140.00 | £125,140.00 |
| HICBC starts | ANI over £60,000 | ANI over £60,000 |
| Full HICBC | £80,000 or more | £80,000 or more |
| HICBC step | 1% per complete £200 | 1% per complete £200 |
| Child Benefit — eldest/only | £26.05 a week | £27.05 a week |
| Child Benefit — additional | £17.25 a week | £17.90 a week |
| Tax-Free Childcare ceiling | Over £100,000 for either partner | Over £100,000 for either partner |
| England working-parent childcare | Changed during year — date logic required | 30 hours/week for 38 weeks, subject to eligibility |
| Tax-Free Childcare top-up cap | £2,000/year; £4,000 disabled child | £2,000/year; £4,000 disabled child |
Update log
20 June 2026 — verified 2026/27 rates, retained 2025/26 historical rates, added complete-£200 HICBC boundaries, explicit pension double-deduction protection and England-only childcare scope.
Official pages are the source of truth
The calculator uses GOV.UK, HMRC and Department for Education pages as primary sources. Adjusted net income comes from HMRC’s Personal Allowances guidance. Personal Allowance and the taper come from the current and previous Income Tax rate pages. HICBC thresholds and the complete-£200-step description come from the High Income Child Benefit Charge guide.
Child Benefit rates come from HMRC’s tax-year rate table rather than a newspaper or commercial tax blog. Tax-Free Childcare and Free Childcare for Working Parents use their current GOV.UK eligibility guides. The Department for Education rollout publication supports the warning that England’s offer changed during 2025/26, while GOV.UK’s Scottish Income Tax page supports the regional tax caveat.
Rates stored by tax year
For both 2025/26 and 2026/27, the standard Personal Allowance is £12,570, the taper begins above £100,000 and the allowance reaches zero at £125,140. HICBC starts over £60,000, rises by one percentage point for every complete £200 of excess and reaches 100% at £80,000. The childcare adjusted-net-income ceiling is over £100,000 for either partner.
The Child Benefit rates differ. For 2025/26, the weekly figures are £26.05 for the eldest or only child and £17.25 for additional children. For 2026/27, they are £27.05 and £17.90. The calculator multiplies each weekly entitlement by 52, producing the approved one-child and two-child examples and clearly describing them as annual estimates.
Published calculation decisions
HICBC uses the formula: excess equals adjusted net income minus £60,000; percentage equals the floor of excess divided by £200; percentage is capped at 100. Income at or below £60,000 returns zero. This makes the boundary examples testable: £60,001 gives 0%, £60,200 gives 1%, £79,999 gives 99% and £80,000 gives 100%.
Childcare income status uses three values. Less than £100,000 is within the income condition, exactly £100,000 is at threshold and over £100,000 is over. The Personal Allowance calculation reduces £12,570 by half of adjusted net income above £100,000 and never goes below zero. The rough tax effect multiplies lost allowance by 40% and is not used for Scotland.
Pension and Gift Aid source treatment
HMRC’s adjusted-net-income page supports grossing up relief-at-source pensions and Gift Aid by the value of basic-rate relief. The implementation divides each net personal amount by 0.8. Qualifying gross pension payments without relief are deducted at the amount paid. Separate fields prevent an already-gross amount from being grossed up again.
Salary sacrifice and net-pay pensions are protected against double deduction through an explicit income-figure choice. Taxable pay after payroll deductions receives no second salary-sacrifice deduction. Gross salary before sacrifice receives one. ‘Not sure’ receives no extra deduction and shows a warning. This conservative behaviour is documented because the same P60 number should never be reduced twice.
Scope and limitations attached to the sources
The Tax-Free Childcare and working-parent childcare pages contain many conditions beyond adjusted net income. The calculator does not convert a within-threshold result into a statement of entitlement. It repeats the work, minimum earnings, child-age, approved-provider, immigration and reconfirmation caveats and directs the user to the official eligibility service.
England’s 30-hour result is not presented as UK-wide. For 2026/27 it states 30 hours a week for 38 weeks for eligible children aged 9 months to 4 years. For 2025/26 it reports a transition and no uniform annual-hours figure. Exact historical hours would need date and term logic that the tax-year selector does not currently collect.
How a future update should be made
A maintainer should first open every official link, record the checked date and compare thresholds, rates, eligibility wording and regional scope. A new tax year should be added as a new rule object rather than overwriting historical data. Source URLs and visible educational copy should be updated together when an official page changes its structure or terminology.
After a rule change, boundary unit tests must be updated or expanded, followed by type checking, linting and a production build. The update log should name the new checked date and material changes. If a source is ambiguous, the interface should say so and avoid calculating a precise result until an authoritative rule supports it. Accuracy takes priority over filling every possible output.
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